Balance wheel assembly

ABSTRACT

In an electronic timepiece the counter weights and magnets are secured to a balance wheel which is stamped from stock material having a uniform thickness throughout. The weight member for distributing the weight in the desired manner is conformed in part to the configuration of the balance wheel and secured directly thereto by adhesives or the like. The magnetic pieces are secured to the weight member and extend through perforations in the balance wheel per se. The perforations may be beveled or formed with a plurality of circumferential fingers to securely grip the magnetic member extending therethrough.

United States Patent Takamune et a1.

[ BALANCE WEEEL ASSEMBLY [72] Inventors: Hirotoki Takamune; Yoshifumi Mochizuki,

21 Appl. No.: 40,654

[30] Foreign Application Priority Data May 28, 1969 Japan ..44/49372 May 29, 1969 Japan ..44/50126 [52] US. Cl. ..58/28 A, 58/107 [51] Int. Cl ..G04b 17/00, G04c 3/04 [58] Field of Search ..58/28 A, 107

[56] References Cited UNITED STATES PATENTS 3,156,857 11/1964 Herr et al ..58/28AX 1 June 20, 1972 3,056,253 10/1962 Beyner et al ..58/28 3,161,012 12/1964 Hug et al. ...58/28 3,186,157 1/1965 Fauret et al ..58/28 Primary ExaminerRichard B. Wilkinson Assistant ExaminerStanley A. Wal Attomey-Sughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT In an electronic timepiece the counter weights and magnets are secured to a balance wheel which is stamped from stock material having a uniform thickness throughout. The weight member for distributing the weight in the desired manner is conformed in part to the configuration of the balance wheel and secured directly thereto by adhesives or the like. The magnetic pieces are secured to the weight member and extend through perforations in the balance wheel per se. The perforations may be beveled or formed with a plurality of circumferential fingers to securely grip the magnetic member extending therethrough.

5 Claims, 13 Drawing Figures PISTEN TEnJuuzo m2 sari: ear 2 BALANCE WHEEL ASSEMBLY This invention generally relates to improvements in and relating to the balance wheel assembly fitted with drive magnet means for cooperation with a battery-driven timepiece having electronic sensing and drive circuit embodied therein.

In the conventional balance wheel assembly of the movable magnet type, drive magnets and at least a counter balance weight are fixedly mounted on the wheel. However, as taught by the practical experiences, the attachment job of the counter balance weight is highly troublesome so that the production cost of this kind of timepieces depends substantially upon the job of the above kind.

A main object of the invention is to provide a balance wheel assembly capable of highly simplifying the manufacture and attachment of the counter balance weight, as well as the drive magnets.

It is a further object of the invention to provide a balance wheel assembly of the above kind for minimizing unavoidable fluctuation of the realized balance from the theoretical, being caused by inaccurate workmanship as well as the fitting of the balance weight to the balance wheel.

In accordance to the invention, the balance wheel proper is prefabricated from an equal thickness plate stock by punching or press job, the openings for attachment of the drive and or sensing magnets being simultaneously formed during the progress of said press job.

It is commonly known that the amount of the unbalance as measured upon completion of the balance wheel assembly should be in the order of several g. cm for keeping the stepping of the timepiece movement at a commercially reacceptable accurate value. However, in practice, the practical amount of the unbalance will amount to the order of as high as several hundreds g. cm, being mainly caused by commonly used degree of workmanship and attachment of the counter weight.

By adopting the novel teachings of the invention, this kind of unbalance will be reduced to a possible minimum.

It is a still further object to provide a balance wheel assembly of such nature as being highly adapted for mass production.

These and further objects, features and advantages of the invention will become more apparent when read the following detailed description of the invention by reference to the accompanying drawings illustrative of several preferred embodiments of the invention.

In the drawings:

FIG. 1 is a sectional plan view of a first embodiment of the invention, the section being taken on the section line A-A shown in FIG. 2.

FIG. 2 is a sectional view of the first embodiment taken on the section line BB shown in FIG. 1.

FIGS. 3 and 4 are similar views to FIGS. 3 and 4 illustrative of the second embodiment, the section being taken along the section lines C-C' and DD', respectively.

FIGS. 5 and 6 are similar views to FIGS. 1 and 2, illustrating, however, a third embodiment of the invention.

FIGS. 7 and 8 are similar views to FIGS. 1 and 2, illustrating, however, a fourth embodiment of the invention.

FIG. 9 is a similar view to FIG. 1, illustrating, however, a fifth embodiment of the invention.

FIG. 10 is a schematic plan view of a modification destined for attaching the drive magnet in position.

FIG. 11 is a sectional view taken along the section line I-I shown in FIG. 10.

FIG. 12 is a still further modified device for attaching a drive magnet in position, the section being taken along the section line K-K shown in FIG. 13.

FIG. 13 is a plan view of the device shown in FIG. 12.

Referring now to FIGS. 1 and 2 of the accompanying drawings, 11 denotes a balance staff which is fitted at a certain mutual distance with two nonferrous balance wheels proper l2 and 12' which are rigidly and tightly attached in turn with magnetic circuit proper 16 and 16', respectively. The tight attachment of balance wheels 12 with the magnetic circuit means 16, for instance, is carried out preferably by sticking or the like conventional measure. The balance wheels 12 and 12' are formed with openings 13 and 13', respectively, in which drive magnets 14 and 14 are rigidly received. In diametral op position to these magnet masses l4 and 14', as a whole and relative to the stafi 11, there is formed a counter balance weight part 15 having a substantial plan dimension.

It should be noted at this stage that the strengthening parts l2; l2 and balance wheels l6; 16' have been formed weight reducing apertures 19, 19' by punching from two overlapped plate stocks at one stroke of a punching press. In the balance wheel 12, the material surrounding the magnet-reception opening 13 is thus continuous with the material consisting the counter balance weight part 15, the thickness of this unitary part being appreciably larger than that of the magnetic circuit means 16. This constructional feature is naturally applied to the remaining balance wheel 12 relative to the reception opening 13 and the magnetic circuit means 16'. In this way, the magnetic circuit means 16 and 16' have been considerably made stiffened. The plate stocks for the balance wheels 12 or 12' and magnetic circuit means 16 or 16' have respective precisely unified thicknesses for obtaining the desired effects.

Conventional hairspring 18, a collet 17 and a stud therefor are also provided for the balance wheel assembly, on and above the latter as seen.

Conventional roller table 21 fitted with an impulse pin 20 is also provided on the lower end part of balance staff 1 l.

The second embodiment shown in FIGS. 3 and 4 has substantially similar constructional features as before. FIG. 3 is a section taken along the section line C-C' in FIG. 4. FIG. 4 is a section along the section line D-D in FIG. 3. In the present embodiment, however, the thickness counter balance weight part 22 or 22' has a larger size than that of the balance wheels 12 or 12. Other parts including those denoted 12 and 12 are similar as before so that same reference numerals are employed.

The counter balance weight part 15 or 15' (FIGS. 1 and 2) has a broader covering area on account of its thickness being equal to the remainder of the balance wheel 12 or 12', respectively. In the present embodiment (FIGS. 3 and 4), however, the diametral width of the counter balance weight part 22 or 22 is substantially smaller than that employed in the first embodiment. Therefore, the whole mass of these parts 22 are positioned substantially nearer to the outside periphery of the whole balance wheel assembly. Therefore, the relationship of the moment of inertia of the assembly to the whole weight thereof is more favorable than before.

It will be seen that when adopting the principles of the invention any bending fabrication is not needed to employ for attaining an increased rigidity of the balance wheel.

It is a further advantage of the invention that there is no need of providing otherwise conventional mount for attaching the balance wheel proper to the balance staff. Therefore, there is no need for glueing fabrication step to attach the balance wheel proper to said conventional kind of mount. These will economize the fabrication of the balance wheel assemblies for use in the electronically driven watches. Next, referring to FIGS. 5 and 6, a third embodiment of the invention will be described.

The numeral 11 represents as before the balance staff. Numerals l2 and 12' represent two separated balance wheels proper prefabricated from nonferrous plate stock of a precisely uniform thickness as before. During the press job; the magnet attaching openings 13 and 13' are formed as before for mounting the cylindrical disc-like sensing and or drive magnets 14 and 14 as before. In the present embodiment, counter balance part 36 or 36' is formed by the provision of a pair of large perforations and 100', each part thus representing a large size and broadly covering, semimoon like shape. The part shown at 32a has been cut away for reducing the whole weight of the assembly. As will be seen, FIG. 5 is a section taken on the line E-E shown in FIG. 6 which is a vertical section taken along the section line FF in FIG. 5.

Magnetic circuit means 35 and 35' covers from outside each pair of said magnets 13 and 13, so as to establish a magnetic circuit including the four magnets and two magnetic plates. Others are similar as before and thus represented by respective same reference numerals as before.

The fourth embodiment shown in FIGS. 7-8, is a slight modification from the foregoing that there is provided only one magnet at 24 or 24 for each wheel proper.

In the fifth embodiment (FIG. 9), the part of the material surrounding each of the magnet 27 and 27' has been cut away, for minimizing a part of the balance wheel. This measure is advantageous for further decreasing the weight of the whole assembly.

FIGS. 10-13 represent several the attaching modes of the magnet to its receiving opening.

In FIG. 10 an arcuate support plate 40 which acts as a magnetic circuit means is secured by means of rivets 42 or the like to the balance wheel 44. The balance wheel 44 is provided with two magnet receiving apertures 46. The walls of the apertures are beveled inwardly in the direction away from the support plate 40 and at their smallest diameter, provide a circular opening having a diameter identical to, or slightly smaller than, the diameter of the magnets 14. The magnets 14 are secured to support plate 40 by any suitable means and extend through the apertures 46 wherein they are securely gripped by the beveled edges, as best seen in FIG. 11.

The embodiment of FIGS. 12 and 13 is similar to the embodiment of FIGS. 10 and 11 with the exception that the beveled edges of the magnet receiving apertures are replaced by a plurality of radially, inwardly directed fingers. In this embodiment, the support plate 40' is secured by means of rivets 42' or the like to the balance wheel 44'. The balance wheel is provided with a magnet receiving aperture 46' and a plurality of inwardly directed fingers 47 are disposed about the aperture 46'. The ends of the fingers 47, define a circular opening having a diameter identical or less than the diameter of the magnet 14. The magnet 14 is secured to the support plate 40' by any suitable means and extends through the aperture into frictional engagement with the fingers 47.

We claim:

1. In a balance wheel assembly for an electrical timepiece, a pair of driving balance wheels disposed in parallel spaced apart relation for oscillation about a common axis, each of said driving balance wheels comprising a circular plate having suitable weight reducing apertures therein intermediate a magnet receiving portion and a counterweight portion, additional plate means secured to one surface of said circular plate in superposed relation thereto, magnet receiving apertures formed in one of said plates, magnet means secured to the other of said plates and extending through said magnet receiving apertures.

2. A driving balance wheel as set forth in claim 1, wherein said additional plate means is substantially coextensive with said magnet receiving portion of said circular plate and is pro vided with an integral one-piece counterweight portion coextensive with the counterweight portion of the circular plate, said magnet receiving apertures being formed in said circular plate.

3. A driving balance wheel as set forth in claim 1, wherein said additional plate means is only coextensive with the magnet receiving portion of said circular plate, said magnet receiving apertures being formed in said circular plate with the magnet means being secured to said additional plate and extending through the apertures in said circular plate.

4. A driving balance wheel as set forth in claim 1, wherein said magnet means are comprised of right cylindrical magnets and said magnet receiving apertures are provided with beveled walls to aid in gripping said magnets.

5. A driving balance wheel as set forth in claim 1, wherein said magnet means are right cylindrical magnets and a plurality of radially inwardly directed fingers are provided about the circumference of said magnet receiving apertures to aid in retaining said magnets in said apertures. 

1. In a balance wheel assembly for an electrical timepiece, a pair of driving balance wheels disposed in parallel spaced apart relation for oscillation about a common axis, each of said driving balance wheels comprising a circular plate having suitable weight reducing apertures therein intermediate a magnet receiving portion and a counterweight portion, additional plate means secured to one surface of said circular plate in superposed relation thereto, magnet receiving apertures formed in one of said plates, magnet means secured to the other of said plates and extending through said magnet receiving apertures.
 2. A driving balance wheel as set forth in claim 1, wherein said additional plate means is substantially coextensive with said magnet receiving portion of said circular plate and is provided with an integral one-piece counterweight portion coextensive with the counterweight portion of the circular plate, said magnet receiving apertures being formed in said circular plate.
 3. A driving balance wheel as set forth in claim 1, wherein said additional plate means is only coextensive with the magnet receiving portion of said circular plate, said magnet receiving apertures being formed in said circular plate with the magnet means being secured to said additional plate and extending through the apertures in said circular plate.
 4. A driving balance wheel as set forth in claim 1, wherein said magnet means are comprised of right cylindrical magnets and said magnet receiving apertures are provided with beveled walls to aid in gripping said magnets.
 5. A driving balance wheel as set forth in claim 1, wherein said magnet means are right cylindrical magnets and a plurality of radially inwardly directed fingers are provided about the circumference of said magnet receiving apertures to aid in retaining said magnets in said apertures. 